Me too. quad core 64 bit system running 8 GB RAM and fresh install on new hard drive of Windows 7. There are exactly 3 programs on this machine. 1.) windows 2.) McAfee 3.) World of Warcraft.
Once a day around 1 PM McAfee mcshield.exe starts gobbling up all available RAM until it reaches ~2GB, then my PC locks up.
Whenever mcupdate kicks in to download the latest DAT file the memory usage increases dramatically. This is probably what you're seeing, and this is why I choose to download DAT files at a time that suits me rather than whenever McAfee detects that an update is available for download. Try changing the settings to disable automatic download and installation of updates and see if it makes a difference.
Is a scan happening then? Does the ram slowly increase or is it only at 2gb when scanning cab and zip files?